Silver halide photographic emulsions containing a copolymer of vinylamine and acrylic acid



United States Patent 3 415,653 SILVER HALIDE PHOTOGRAPHIC EMULSIONS CONTAINING A COPOLYMER OF VINYL- AMINE AND ACRYLIC ACID Donald A. Smith and Ernest J. Perry, Rochester, N.Y., assignors to Eastman Kodak Company, Rochester, N.Y., a corporation of New Jersey No Drawing. Filed Dec. 21, 1964, Ser. No. 420,145 2 Claims. (Cl. 96-114) ABSTRACT OF THE DISCLOSURE In preparation of photographic silver halide emulsions, silver halide is emulsified by reacting soluble silver salt and soluble halide salt to form silver halide in aqueous medium with a peptizer in solution. The peptizer is a copolymer comprising vinylamine units and acrylic acid units in mole ratio in the range from l.0:l.0 to 1.8:l.0. In some embodiments the copolymer can further comprise up to 5 molar parts ethyl acrylate.

This invention relates to silver halide dispersions, and more particularly to a method of preparing silver halide dispersions which involves precipitating silver halide in the presence of certain peptizers.

It is well known that the first step in the preparation of photgraphic emulsions involves preparing silver halide by a double decomposition reaction of soluble silver salts and alkali halide salts usually in the presence of a peptizer with or without ammonia. Effective peptization (1) prevents the insoluble silver halide from preciptating in the form of coarse crystals, which, because of excessive graininess, would be useless in photographic emulsion layers; and (2) prevents clumping and aggregation of the emulsion crystals thus preventing gross irregularities and the occurrence of infectious development in the developed photographic emulsion layers. Elfective peptization permits proper growth of the silver halide emulsion crystals during preparation of the emulsion, the size distributions resulting from this growth having a decisive influence on basic sensitometric properties, i.e., speed, contrast, graininess, acutance and the like.

While gelatin is a satisfactory peptizer, its use has a number of inherent disadvantages. Being a naturally occurring material, it is rather sensitive to bacterial attack and its uniformity is questionable due to the variety of sources from which it is obtained. The compatibility of gelatin with other polymeric vehicles which may provide coatings having superior physical properties is also limited. In addition, it is desirable to be able to obtain emulsion crystals which have photographically significant differences in crystal structure and size distribution as compared to those obtained when gelatin is employed as peptizer.

Most of the polymers which have heretofore been suggested as peptizers for silver halides have not functioned satisfactorily. In many instances, they have not produced effective peptization, which results in clumping and aggregation of the emulsion grains. In other instances, for example, with poly(vinyl alcohol) or polyvinyl pyrrolidone, restraint of grain growth by the peptizer has rendered it impossible to obtain sufficiently large, well-shaped emulsion crystals having satisfactory photographic characteristics.

One object of our invention is to provide polymeric peptizers for silver halide dispersions. Another object of our invention is to provide polymeric peptizers for silver halide dispersions, which peptizers result in silver halide crystals having photographically significant differences in crystal structure as compared to those obtained when gelatin is employed as peptizer. A further object of our invention is to provide certain terpolymers which function as peptizers for silver halide dispersions. Other objects of our invention will appear herein.

These and other objects of our invention are accomplished by the method of preparing silver halide dispersions which comprises reacting a water soluble silver salt with a water soluble halide salt in an aqueous solution containing a copolymer of vinylamine and acrylic acid having a molar ratio of vinylamine to acrylic acid within the range of from 10:10 to 1.8:1.0. (All polymer compositions herein and in the appended claims are given in terms of molar ratios of the monomer units.)

In another embodiment of our invention, we provide a method of preparing silver halide dispersions which comprises incorporating a water soluble halide salt in an aqueous ammoniacal solution of silver nitrate and a terpolymer containing from 1.0 to 1.8 molar parts vinylamine, from 1.8 to 1.0 molar parts acrylic acid and 0 to 5 molar part ethyl acrylate.

We have found that the copolymers and terpolymers employed as peptizers in accordance with our invention provide excellent silver halide dispersions, the silver halide crystals of which differ significantly in photographic characteristics from the silver halide crystals obtained when gelatin is employed as peptizer.

Our invention will be illustrated by the following examples, which also demonstrate the critical relationship between the ratio of vinylamine to acrylic acid in the copolymers. Examples l5 show the use of copolymers of vinylamine and acrylic acid as peptizers for silver halide. Examples 1 and 2 show that copoly(vinylamineacrylic acid) polymers which have a vinylamine to acrylic acid molar ratio between l.0:l.8 and 1.01333 have no peptizing effect.

EXAMPLE 1 1.0/3.33 molar ratio copolymer of vinylamine and acrylic acid A solution of 7.15 g. of t-butyl vinylcarbamate and 16.7 g. of acrylic acid in ml. of dioxane was treated with 0.3 g. azobisisobutyronitrile (ABIN) and flushed with nitrogen. The polymerization was carried out at 60 for 18 hours, yielding a viscous, colorless dope. A small portion of this was poured into ether and the precipitated intermediate polymer isolated for analysis.

Found: C, 52.5; H, 7.0; N, 2.9.

The balance of the dioxane solution was treated with ml. of acetic acid and concentrated in vacuo to a near solid. An additional 200 ml. of acetic acid was added and the solution was heated to 60. Removal of the carbamate blocking group was accomplished by the addition of 5 ml. of concentrated sulfuric acid. The viny1amineacrylic acid copolymer which separated was collected and purified by solution in methanol and precipitation in ether.

Found: C, 45.9; H, 7.6; N, 2.9.

The preparation of a neutral emulsion was carried out in the following manner. An aqueous solution, the volume of which was equal to 30 ml. and which contained 3.275 g. potassium bromide, 0.1 g. potassium iodide and 1.0 g. of the 1.0/ 3.33 molar ratio copolymer of vinylamine and acrylic acid was equilibrated at 70. Twenty ml. of an aqueous solution containing 3.82 g. silver nitrate was then added over a period of 30 minutes. The reaction mixture was stirred throughout the addition of the silver nitrate and for a further 30-minute period after addition was complete. The temperature of the emulsion was kept at 70 during both stages of emulsion preparation. The emulsion obtained was completely unstable which indicates that the 1.0/3.33 molar ratio copolymer of vinylamine and acrylic acid has no peptizing action in neutral silver halide emulsions.

EXAMPLE 2 1.0/1.8 molar ratio copolymer of vinylamine and acrylic acid Twenty-two grams of t-butyl vinylcarbamate and 19.9 g. of acrylic acid were polymerized in the same manner as in Example 1. However, in this case the entire intermediate product was isolated by precipitation in ether the product weighed 10.2 g.

Found: C, 40.9; H, 6.2; N, 11.2.

Twenty grams of the above copolymer was dissolved in 100 ml. of acetic acid at 60 and treated with ml. of concentrated nitric acid. This gave a rapid evolution of carbon dioxide and separation of solid material. The liquid was decanted and the solid dissolved in water and precipitated in isopropyl alcohol. After vacuum drying the product weighed 10.2 g.

Found: C, 40.9; H, 62.; N, 11.2.

A neutral emulsion was prepared as described in Example 1 except that the peptizer used was the 1.0/1.8 molar ratio copolymer of vinylamine and acrylic acid. The total instability of the emulsion obtained indicates that the 1.0/1.8 molar ratio copolymer of vinylamine and acrylic acid is completely ineifective as far as peptization of neutral silver halide emulsions is concerned.

Examples 3 and 4 demonstrate the use of copolymers of vinylamine and acrylic acid as peptizers in accordance with the present invention.

EXAMPLE 3 1.0/1.0 molar ratio copolymer of vinylamine and acrylic acid In the same manner as in Example 2, 34.0 g. of t-butyl vinylcarbamate and 17.2 g. of acrylic acid were copolymerized to yield 43.5 g. of product.

Found: C, 54.0; H, 7.8; N, 5.4.

A solution of g. of the above copolymer in acetic acid was treated at 60 with 15 ml. of nitric acid, precipitating a colorless solid which was purified as before yielding 14.6 g. of product.

Found: C, 3.90; H, 7.0; N, 10.6.

A neutral emulsion was prepared as described in Example 1 except that the peptizer used to prepare the emulsion was the 1.0/ 1.0 molar ratio copolymer of vinylamine and acrylic acid. The emulsion obtained showed excellent stability and was completely free from any undesirable clumping, aggregation, or sedimentation effects. The emulsion grains constituting this emulsion were tabular octahedral crystals with diameters ranging from 0.4 to 4.2 microns. The average diameter was 1.03 microns.

EXAMPLE 4 1.8/1.0 molar ratio copolymer of vinylamine and acrylic acid In the same manner as in Example 2, 28.0 g. of t-butyl vinylcarbamate and 7.84 g. of acrylic acid were copolymerized to yield 28 g. of product.

Found: C, 53.7; H, 8.0; N, 6.5.

A 20 g. portion of the above was treated with 19 m1. of nitric acid as in Example 2, yielding 18.5 g. of reprecipitated copolymer.

Found: C, 44.1; H, 8.6; N, 9.1.

A neutral emulsion was prepared according to the method given in Example 1 except that the peptizer used to prepare the emulsion was the 1.8/1.0 molar ratio copolymer of vinylamine and acrylic acid. The very eiTec- -tive peptizing action of this composition is evident from the excellent stability of the emulsion obtained which was free from any undesirable clumping or aggregation effects. The emulsion grains consisted of tabular octahedral crystals with diameters ranging from 0.3 to 4.2 microns. The average grain diameter was equal to 1.16 microns.

Example 5 demonstrates that copolymers containing a vinylamine to acrylic acid molar ratio of 3.33 to 1.0 provides unsatisfactory pepitization due to clumping between the emulsion grain.

EXAMPLE 5 3.33/10 molar ratio copolymer of vinylamine and acrylic acid In the same manner as Example 2, 26.0 g. of t-butyl vinylcarbamate and 3.95 g. of acrylic acid were copolymerized to yield 16 g. of polymer.

Found: C, 55.3; H, 7.8; N, 6.6.

All but a small sample of this product was cleaved in the usual manner with nitric acid and the product which precipitated was washed thoroughly with isopropyl alcohol and dried in vacuo, yield, 12.8 g.

Found: C, 35.0; H, 6.1; N, 12.8.

A. neutral emulsion was prepared according to the method described in Example 1 except that the peptizer used to prepare the emulsion was the 3.33/10 molar ratio copolymer of vinylamine and acrylic acid. The unsatisfactory performance of this material with regard to silver halide peptization and control over grain growth was evident from the fact that the grains of this emulsion were clumped to a very considerable extent. The emulsion grains were small and mostly of roughly spherical shape indicating that this polymer restrains normal emulsion grain growth and also inhibits the formation of octahedral crystals.

Examples 6-10 show the use of copoly(vinylamineacrylic acid) polymers as peptizers for silver halide. In these examples, different molar ratios of vinylamine to acrylic acid were employed. The results obtained with the copolymers employed in Examples 79 were good, whereas the results obtained in Examples 6 and 10 were unacceptable, the molar ratio of vinylamine to acrylic acid in the copolymers employed in these examples not being within the range useful in accordance with the invention.

EXAMPLE 6 The following method was used to prepare an ammoniacal emulsion. An aqueous solution (volume equal to 20.0 ml.) was prepared which contained 3.82 g. silver nitrate and an amount of ammonium hydroxide just sufficient to redissolve the precipitate which had formed initially on addition of the ammonium hydroxide to the silver nitrate solutions. This solution was added over a period of seconds to 30 ml. of a continuously stirred solution containing 3.14 g. potassium bromide, 0.1 g. potassium iodide and 1.0 g. of the 1.0/3.33 molar ratio copolymer of vinylamine and acrylic acid, described in Example 1. Stirring of the emulsion was then continued for an additional 39-minute period. Throughout the addition of the silver nitrate solution as well as during the subsequent stirring period, the temperature of the reaction mixture was held at 45. The emulsion obtained was completely unstable which indicates that the 1.0/ 3.33 molar ratio copolymer of vinylamine and acrylic acid has no peptizing effect in ammoniacal silver halide emulsions.

EXAMPLE 7 An ammoniacal emulsion was prepared as described in Example 6 except that the peptizer used to prepare this emulsion was the 1.0/ 1.8 molar ratio copolymer of vinyl amine and acrylic acid described in Example 2. The emulsion obtained showed excellent stability and was free from any undesirable clumping, aggregation or sedimentation effects. The grains constituting this emulsion were fairly uniformly sized crystals mostly of cubic or rounded-cubic shape. The grain size diameters were within the range 0.751.6 microns; the average grain size diameter Was 0.89 micron.

EXAMPLE 8 An ammoniacal emulsion was prepared as described in Example 6 except that the peptizer used for the preparation of this emulsion was the 1.0/1.0 molar ratio copolymer of vinylamine and acrylic acid described in Example 3. The emulsion obtained showed excellent stability and was free from any undesirable clumping, aggregation or sedimentations efr'ects. After 20 minutes of ripening (i.e., 20 minutes as measured from the beginning of silver halide precipitation) the emulsion grains fell into one of two size classes: (1) a small size class, average diameter 0.28 micron, and consisting of cubic grains; and (2) a larger size class, characterized by an average grain diameter of 0.66 micron, and showing one of the following crystalline forms: cubic, twinned-cubic (of triangular shape), or bar-shaped. After emulsion preparation was complete (i.e., 40 minutes from the time when emulsion precipitation was begun), the average diameter of the small grain size class had not changed, while the average grain size diameter of the larger grain size class had grown to 0.88 micron.

EXAMPLE 9 An ammoniacal emulsion was prepared as described in Example 6 except that the peptizer used to prepare this emulsion was the 1.8/ 1.0 molar ratio copolymer of vinylamine and acrylic acid, described in Example 4. The resulting emulsion showed excellent stability and was free from any undesirable clumping, aggregation or sedimentation effects. Some restraining effect of the polymeric peptizer on emulsion grain growth was evident as the average grain diameter of the emulsion was equal to 0.32 micron. Most of the emulsion grains were cube-shaped.

EXAMPLE 10 An ammoniacal emulsion was prepared as described in Example 6 except that the peptizer used to prepare this emulsion was the 3.33/1.0 molar ratio copolymer of vinylamine and acrylic acid described in Example 5. The in effectiveness of this polymer as a peptizer for converted silver halide emulsions was evident from the very extensive clumping between emulsion grains which had occurred. The grain size of the emulsion indicated that this polymer exerts strong restraint on emulsion grain growth.

EXAMPLE 11 This example shows the use of terpolymers of vinylamine, acrylic acid and ethyl acrylate as peptizers for silver halide. The terpolymers were prepared essentially the same as the copolymers of vinylamine and acrylic acid, by solution polymerization in acetone using ABIN as catalyst. The acid catalyzed removal of the blocking group was carried out without isolation of the first copolymer, the acetone being displaced by acetic acid through vacuum concentration. Three neutral emulsions were prepared as described in Example 1 using terpolymers containing (1) 3.2 molar parts ethyl acrylate, 1.0 molar part vinylamine and 1.67 molar parts acrylic acid; (2) 1 molar part each of ethyl acrylate, vinylamine and acrylic acid; and (3) 3.2 molar parts ethyl acrylate, 1.8 molar parts vinylamine and 1.0 molar parts acrylic acid. No peptization resulted in using terpolymers (1) and (3). The terpolymer containing equal molar parts of ethyl acrylate, vinylamine and acrylic acid, while providing some peptization, was not regarded satisfactory due to partial sedimentation and some clumping of the silver halide. Ammoniacal emulsions were prepared as described in Example 6 with the three terpolymers. Excellent peptization occurred with each of the terpolymers.

In certain applications, the combined effect of copoly- (vinylamine-acrylic acid) and gelatin is important. It is desirable to enhance the rate of solution of silver halide grains in a gelatin layer containing silver halide grains to be used for the production of images in a nucleated receiving layer by diffusion transfer processes. This increase in the rate of silver halide solution makes a larger concentration of silver ions available for difiusion into the receiving layer of the diffusion transfer system, and accelerates the rate of physical development of the silver ion in the nucleated receiving layer containing gelatin as the vehicle. Both processes are critically and uniquely affected by the vinylamine to acrylic acid molar ratio of copoly(vinylamine-acrylic acid) polymers when combined with gelatin either in the silver halide emulsion layer or in nucleated receiving layer-s of the type used in diffusion transfer processes.

The rate of physical development in a system in which silver ions furnished by dissolution of silver halide grains subsequently undergo physical development at the surface of catalytic nuclei is controlled by two processes. First, the rate at which silver ions become available for subsequent physical development; secondly, the rate at which these ions are reduced at the catalytic surface during physical development, Example 12 shows the critical dependence of the rate of solution of silver halide grains which are suspended in a mixture of gelatin and copoly(vinylamineacrylic acid) on the vinylamine to acrylic acid molar ratio in the copolymer. Example 13 demonstrates that the rate at which a constant concentration of silver ions is physically developed at the catalytic surface of nuclei which are suspended in a mixture of gelatin and copoly(vinylamine-acryli-c acid) is critically dependent on the molar ratio of vinylamine to acrylic acid in the copolymer. Results from a diffusion transfer experiment are described in Example 14.

EXAMPLE 12 The relative rates of solution of silver halide crystals suspended in a solution of either gelatin or of one of several gelatin/polymer mixtures was measured in accordance with the method described by E. J. Perry, Phot. Sci. Eng. 5, 349 (1961). The following results were obtained:

Relative Rate of solution of peptized silver halide crystals Peptizer Gelatin 4/1 mixture of gelatin and of 1.0/3.33 molar ratio copoly mer of vinylamine and acrylic acid (described in Example 1) 4/1 mixture of gelatin and of 1.0/1.0 molar ratio copolymer of vinylamine and acrylic acid (described in Example 3) 4/1 mixture of gelatin and of 3.33/10 molar ratio copolymer of vinylamine and acrylic acid (described in Example 5) These results show that the effectiveness of a vinylamine-acrylic acid copolymer with respect to bringing about a substantial increase in the rate of solution of silver halide crystals peptized by a mixture of gelatin and of copoly(vinylamine-acrylic acid) depend critically on the vinylamine-acrylic acid molar ratio of the copolymer.

EXAMPLE 13 Relative rate of physical development of a constant silver ion concentration Peptizer Gelatin 4/1 mixture of gelatin and of 1.0/3.33 molar ratio copolymer of vinylamine and acrylic acid (described in Example 1) 4/1 mixture of gelatin and of 1.0/1.0 molar ratio copolymer oi vinylamine and acrylic acid (described in Example 3) 4/1 mixture of gelatin and 01 33311.0 molar ratio copolymer of vinylamine and acrylic acid (described in Example 5) These results show that the magnitude of the physical development enhancement effect depends critically on the vinylamine-acrylic acid molar ratio in the copolymer.

EXAMPLE 14 A receiving layer suitable for diffusion transfer of soluble silver ions from a silver halide layer and subsequent physical development of these ions in the receiving layer was prepared in the following manner. To 25 ml. of a solution containing 0.4 g. gelatin and 0.1 g. of the 1.0/ 1.8 copolymer of vinylamine and acrylic acid, described in Example 2, there was added 1.25 ml. of a suspension (1 g./liter) of silver nuclei (Silver Protein Mild made by Mallinckrodt Chemical Works), 0.4 ml. of five percent saponin solution and 0.5 ml. of a 0.314 percent formaldehyde solution. The resulting mixture was then coated on reflection print support by means of a coating knife which had a clearance of 0.003 inch. The dried coating was then processed in the following manner in a dark room illuminated by red light.

A strip of unexposed Kodak Fine Grain Positive Film was immersed for three seconds in a developer of the following composition:

G. Elon 6.25 Hydroquinone 2.50 Sodium sulfite 6.25 Sodium thiosulfate pentahydrate 7.70 Potassium bromide 1.02

Sodium carbonate monohydrate 25.00 Water to make one liter.

After removal of the strip of Kodak Fine Grain Positive Film from this developer, the film was pressed for exactly 20 seconds against the receiving layer described above. After completion of this 20-second period of contact, the receiving layer Was dried. X-ray spectrometric analysis then showed that the receiving layer contained 3.8 mg. silver per square foot of receiving layer.

A second receiving layer was prepared exactly as described above except that the polymer admixed to the gelatin was the 3.33/1.0 molar ratio copolymer of vinylamine and acrylic acid described in Example 5. After the processing sequence described above, the receiving layer containing the 3.33/1.0 molar ratio copolymer of vinylamine and acrylic acid contained 13.3 mg. silver per square foot of receiving layer, i.e., 3.5 times as much as the receiving layer containing the 1.0/1.8 molar ratio copolymer of vinylamine and acrylic acid.

The copolymers and terpolymers which we employ in according with our invention may have a wide molecular weight range, such as from about 5,000 to 500,000. The concentration of the ploymeric peptizers in the solution in which the silver halide is precipitated may range from about 0.07 to 0.35 part based on the weight of the silver halide to be precipitated. However, this concentration may be varied over a considerable range as desired.

The invention has been described in detail with particular reference to preferred embodiments thereof but it will be understood that variations and modifications can be effected within the spirit and scope of the invention as described hereinabove and as defined in the appended claims.

We claim:

1. A method of preparing silver halide dispersions which comprises reacting a Water soluble silver salt with a Water soluble halide salt in an aqueous solution containing a copolymer of cinylamine and acrylic acid having a molar ratio of vinylamine to acrylic acid within the range of 1.0210 to 1.8:1.0.

2. The method of preparing a silver halide dispersion which comprises forming an aqueous solution of silver nitrate and a terpolymer containing from 1.0 to 1.8 molar parts vinylamine, from 1.8 to 1.0 molar parts acrylic acid and from 0 to 5 molar parts ethylacrylate, said solution containing just sufiicient quantity of ammonium hydroxide to redissolve the precipitate which forms upon the initial addition of the ammonium hydroxide to the aqueous silver nitrate solution, and incorporating in said solution a water soluble halide salt.

References Cited UNITED STATES PATENTS 2,949,442 8/1960 Clavier et al. 96114 FOREIGN PATENTS 540,976 9/ 1955 Belgium. 752,290 7/ 1956 Great Britain.

I. TRAVIS BROWN, Primary Examiner.

US. Cl. X.R. 96-94 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 ,415 ,653 December 10 1968 Donald A. Smith, et al.

It is certified that error appears in the above identified patent and that said Letters Patent are hereby corrected as shown below:

line 9, "the product weighed 10.2 g." should read and yielded on drying 39.7 g. line 10, "Found: C, 40.9; H, 6,2; N, 11.2." should read Found: C, 52.8 H, 7.5 N, 4.3. line 18, "H, 62. should read H, 6.2

Signed and sealed this 24th day of March 1970.

Column 3,

(SEAL) Attest:

Edward M. Fletcher, Jr.

Commissioner of Patents Attesting Officer WILLIAM E. SCHUYLER, JR. 

